Automatic steering for unmanned vehicles, either naval, aerial or ground vehicles exist. During most of the time driving the vehicle around is a rather simple task for most automatic systems, but for more sophisticated tasks, such as taking-off, landing, docking, parking, and air-refueling (these are merely examples of sophisticated tasks) high-accuracy and fast response time are needed.
In most cases, improper maneuvering may cause capital loss.
Many maneuvers can be executed automatically, provided that the guidance system has access to real-time data on the absolute or relative position of the vehicle, approach path and velocity. If programmed correctly, automatic maneuvering systems can make all required decisions without mistakes, thus eliminating the risk of failure due to human error. In addition, automatic maneuvering systems replace trained personnel, thus reducing operation expenses. These facts motivate the use of automatic maneuvering systems.
For low-flying aircraft, such as Unmanned Aerial Vehicles (UAV's), the position signal (for example GPS) is of the same order of magnitude as the error that occurs when calculating velocities and is derived from position error multiplied by the sampling rate. At low altitudes changes in side wind heavily influence the UAV position, thus seriously affecting the reliability of tracking and guidance of the UAV using currently available positioning systems.
For example, most of the UAV's takeoffs and landings are presently human assisted. An external human pilot stands near the runway, watches the vehicle and controls it through the use of a remote control.
An autopilot system guided by a static (land) laser beacon is disclosed in U.S. Pat. No. 6,456,910. The beacon consists of a laser beam shaped as a narrow vertical fan beam that is illuminated in a fixed direction. The vehicle is equipped with a linear photo-detector array spanning the whole vehicle width. This array detects the distance between the beacon beam and the sensor array center, thus deriving a correction signal. This correction signal is fed into the vehicle steering actuator, which corrects the vehicle trajectory to position its center on the beacon beam. The disadvantage in this system is the fact that the beam direction is fixed, and this means that in order to effectively employ this system the vehicle must be limited to a narrow approach path, which is defined by the width of the sensor array. If the beam is not on the array the system is ineffective.
An autopilot system for UAVs is commercially offered by Ruag Aerospace (Switzerland) and called OPATS. This system uses a passive retro-responder on the airplane, and a land based instrument capable of measuring the distance and the azimuth-elevation angles to this responder, thus determining the 3D position of the vehicle in a fixed coordinate system relative to the runaway, much like a RADAR system (only using optical beam rather than RF). The land based instrument is responsible for deriving the location of the UAV and for transmitting control information to the UAV based on the derived location.
It is an object of the present invention to provide a novel accurate positioning system (and method) effective over a broad sector, whose accuracy is fixed and not affected by the size of the broad sector.
Another object of the present invention is to provide such positioning system that is vehicle-based, offering local independence and control, eliminating the need for control signals from an off-board location.
Other objects and advantages will become clear after reading the present specification and considering the accompanying drawings.